Aww bless you OP.
My DH also proposed with a ring that is completely not my taste.
It's so hard, because on one hand, your DH proposed, and went to the effort to pick out a nice surprise engagement ring for you, to show how much he loves you, and that he wants to spend his life with you.
However, having to wear something that isn't your taste can feel tricky and a bit upsetting.
In the end I told my DH I appreciated the thought he put into it, but it wasn't really my taste (it's very quirky, like me, but I wanted a classic engagement ring). DH wasn't able to return the ring, and I felt awful as he'd spent a fair bit, so in the end I've learned to love it. Reflecting, I also feel like I was acting like a spoilt brat, I should be happy he put thought, effort and £ into a ring he thought I would love. I should've accepted it gratefully tbh as he is such a sweet and caring man.
Nowadays I don't even think about it, I love my DH, we're happily married and have much bigger things to worry about/spend our money on (a baby!).
Ultimately, if you really can't wear it, one option might be to get a bigger wedding ring, and just wear that instead, and keep the engagement ring in your jewellery box?